Methods of measurement include the use of one-dimensional mechanical devices which measure from point to point along a straight line. Vernier measuring devices utilize relatively movable scales where one scale has a slightly differing pitch or spacing of its indicia than the pitch or spacing of the indicia on the other scale. Usually the moving scale is provided with indicia having a different pitch than the indicia on the stationary scale. For example, the moving scale can have indicia with a pitch of 0.9 times the pitch of the indicia on the stationary scale. Thus with eleven scale marks or indicia on the moving scale, the first and the eleventh marks on the moving scale align with the first and the tenth marks or indicia on the stationary scale. Then as the moving scale is shifted to another position relative to the fixed scale, an alignment of a scale mark (between one and eleven) on the moving scale will occur with a scale mark on the fixed scale. The matching mark of the moving scale with a mark on the fixed scale denotes the fractional or decimal part of the stationary scale through which the moving scale has moved. By designating the first mark as zero ("0") and the eleventh mark as ten ("10") the fractional part can be measured in tenths of the base scale.
In some instances, the relative positioning of an object point or location on a screen, scope or map in terms of cartesian coordinates can be desired which requires location in both the X and the Y directions. Heretofore, the location between grids was based principally upon approximation rather than measurement.